Subterranean termites (family Rhinotermitidae) are major decomposers of wood and other cellulosic materials. Since subterranean termites construct their nests not only in soil, but in dead wood, including wooden structures, they are major insect pests. Conventional methods for termite control have focused on the application of toxic synthetic organic chemicals, such as pyrethroids. These chemicals are typically applied as a barrier to prevent entry of termites into wooden structures, and/or directly to termite colonies by drilling into subterranean termite nests. However, the introduction of pesticides into the characteristically extensive colonies of subterranean termites by such conventional means is unreliable. Effective control is difficult to assess, greater amounts of pesticides are likely to be used than are necessary, and the prevention or elimination of a building infestation may not seriously affect the source colony.
Another, more recently applied, subterranean termite control strategy involves the use of poisoned baits. DowElanco (now Dow AgroSciences) has developed a poisoned bait subterranean termite control system called Sentricon.TM.. The Sentricon.TM. system typically includes several termite colony elimination stations. Each station is composed of a plastic tube (housing) about 4 by 24 cm with a removable top cap. Typically, a number of Sentricon.TM. stations are inserted into the ground in the region of a subterranean termite colony, and a termiticide-treated bait material is placed in each station housing. The Sentricon.TM. system uses Dow AgroSciences' Recruit.TM. II Baitube.TM. devices containing approximately 30 g of cellulose material impregnated with 0.5% (w/w) hexaflumuron as the bait material. Hexaflumuron acts as an insect growth regulator (IGR), inhibiting the normal molting process of the termites, resulting in death. The success of the Sentricon.TM. system in eliminating colonies of several species of subterranean termites has been documented.
Research on the chemical basis of food selection for many major agricultural insect pests has led to improved understanding of feeding behaviors. This has in turn suggested improved monitoring and control strategies. An example of this is the corn rootworm, Diabrotica undecimpunctata, for which both monitoring and toxic bait techniques have been developed based on knowledge of the chemical basis of food selection. Incorporation of a subterranean termite feeding stimulant into a termiticide-treated bait has the potential to selectively target termite colonies and enhance control of cryptic subterranean termites. Such an approach would also take advantage of the food exchanging behavior (trophallaxis) characteristic of subterranean termites. However, very little is known about the chemical and environmental cues used in food selection by subterranean termites, and compositions which stimulate feeding of subterranean termites have not previously been identified.
The widespread observation that termites coexist with fungi in dead wood suggests that fungi enhance the wood's value for the termites (Hendee, E. C. (1934). The Role of Fungi in the Diet of Termites. Science 80(2075): 316; Kovoor, J. (1964). Modifications chimiques provoques par un termitidae (Microtermes edentalus, Was.) dans du bois de peuplier sain ou partiellement degrade par des champignons. Bull. Biol. Fr. Belg. 98: 491-510). Wood structures infested with subterranean termites characteristically also exhibit some fungal presence in close proximity to the termites (Hendee, E. C. (1933). The Association of the Termites, Kalotermes minor, Reticulitermes hesperus, and Zootermopsis angusticollis with Fungi. University of California Publications in Zoology 39: 111-133). In field settings, termites are never found without numerous intimately associated fungi, although due to the abundance of fungi in these habitats, this is expected. Since fungi are ubiquitous in soils and dead wood in forested areas, these organisms clearly coexist with subterranean termites in soils and wood. Among the possible influences of fungi on termite ecology are induction of trail-following, directed foraging, and feeding stimulation. For example, fungi may modify the chemical composition of wood as their mycelia penetrate and digest it, incorporating nitrogen and other nutrients into this material, partially pre-digest complex polymeric compounds, or degrade toxic and repellent constituents, any of which could lead to increased feeding and survival of termites.
Both field observations and laboratory experiments with fungal extracts indicate that termite behaviors can be affected by compounds produced by certain fungal species (Esenther, G. R., T. C. Allen, et al. (1961). Termite attractant from fungus-infected wood. Science 134(3471): 50; Watanabe, T. and J. E. Casida (1963). Response of Reticulitermes flavipes to fractions from fungus-infected wood and synthetic chemicals. Journal of Economic Entomology 56: 300-307). For example, certain basidiomycete fungi are known to produce substances that elicit trail-following in Rhinotermitidae in laboratory assays; i.e., Gloeophyllum trabeum (Matsumura, F., Tai, A., & Coppel, H. C. (1969). Termite Trail-Following Substance, Isolation, and Purification from Reticulitermes virginicus and Fungus-Infected Wood. Journal of Economic Entomology 62: 599-603; Amburgey, T. and R. V. Smythe (1977a). Factors influencing termite feeding on brown-rotted wood. Sociobiology 3(1): 3-12), Oligoporous balsameus (Grace, J. K. and W. W. Wilcox (1988). Isolation and trail-following bioassay of a decay fungus associated with Reticulitermes hesperus Banks. Pan-Pacific Entomologist 64(3): 243-249) and Serpula lacrimans (among others) (Matsuo, H. and K. Nishimoto (1975). Response of the Termite Coptotermes formosanus (Shiraki) to Extracts Fractions from Fungus-infected Wood and Fungus Mycelium. Matererial und Organismen 9: 225-238), although any possible ecological consequences of fungal synthesis of the termite trail-following substances are unknown, and this discovery has not been successfully exploited for termite control. Deleterious effects of fungal extracts on termite feeding and survival have also been shown (Kovoor 1964; Sands, W. A. (1969). The Association of Termites and Fungi. Biology of Termites. K. &. W. Krishna F. A. New York, Academic Press. I: 495-524; Matsuo and Nishimoto 1975; Moein, S. I. and M. K. Rust (1992). The Effect of Wood Degradation by Fungi on the Feeding and Survival of the West Indian Drywood Termite, Cryptotermes brevis (Isoptera: Kalotermitidae). Sociobiology 20: 29-39). However, despite numerous studies of subterranean termites and fungi (Sands 1969; Becker, G. (1976). Termites and Fungi. Material und Organismen Beiheft 3: 465-478; Amburgey, T. (1979). Review and checklist of the literature on interactions between wood-inhabiting fungi and subterranean termites. Sociobiology 4(2): 279-296), the implications of joint occupancy have never been adequately explained, and no truly phagostimulatory (feeding-stimulating) or phagodeterrent fungal metabolites have been identified.
Accordingly, it would be desirable to isolate a subterranean termite feeding stimulant, and to incorporate such a feeding stimulant into termiticide-treated bait-based systems and methods to selectively target and enhance control of subterranean termites.